Swiftジャイロスコープ：オプション値のアンラップ中に予期せずnilが見つかりました

Core Motionを使用していて、「オプションの値をアンラップしているときに予期せずnilが見つかりました」というメッセージが表示されますが、アプリをロードする時間の約半分しかありません。以下のコードを修正して安定させるにはどうすればよいですか？

import UIKit
import CoreMotion

class ViewController: UIViewController {

var currentMaxRotX: Double = 0.0
var currentMaxRotY: Double = 0.0
var currentMaxRotZ: Double = 0.0

let motionManager = CMMotionManager()

@IBOutlet var RollLabel: UILabel!
@IBOutlet var PitchLabel: UILabel!
@IBOutlet var YawLabel: UILabel!

@IBOutlet var rotX: UILabel!
@IBOutlet var rotY: UILabel!
@IBOutlet var rotZ: UILabel!

@IBOutlet var maxRotX: UILabel!
@IBOutlet var maxRotY: UILabel!
@IBOutlet var maxRotZ: UILabel!


@IBOutlet var readOutLabel: UILabel!

override func viewDidLoad() {

    if motionManager.gyroAvailable {

        motionManager.startGyroUpdates()
        motionManager.deviceMotionUpdateInterval = 0.2
        motionManager.startDeviceMotionUpdates()

        motionManager.gyroUpdateInterval = 0.2
        motionManager.startGyroUpdatesToQueue(NSOperationQueue.currentQueue()) {
            [weak self] (gyroData: CMGyroData!, error: NSError!) in

            if self?.outputRotationData(gyroData.rotationRate) != nil {

            self?.outputRotationData(gyroData.rotationRate)
            if error != nil {
                println("\(error)")
            }

        }
        }

    } else {
        println("gyro not avail")
    }

    super.viewDidLoad()
}
// radians to degrees
func radians(fromDegrees degrees: Double) -> Double {
    return 180 * degrees / M_PI
}

func outputRotationData(rotation:CMRotationRate)
{
    rotX.text = NSString(format:"Rotation X: %.4f",rotation.x) as String
    if fabs(rotation.x) > fabs(currentMaxRotX)
    {
        currentMaxRotX = rotation.x
    }

    rotY.text = NSString(format:"Rotation Y: %.4f", rotation.y) as String
    if fabs(rotation.y) > fabs(currentMaxRotY)
    {
        currentMaxRotY = rotation.y
    }
    rotZ.text = NSString(format:"Rotation Z:%.4f", rotation.z) as String
    if fabs(rotation.z) > fabs(currentMaxRotZ)
    {
        currentMaxRotZ = rotation.z
    }

    maxRotX.text = NSString(format:"Max rotation X: %.4f", currentMaxRotX) as String
    maxRotY.text = NSString(format:"Max rotation Y:%.4f", currentMaxRotY) as String
    maxRotZ.text = NSString(format:"Max rotation Z:%.4f", currentMaxRotZ) as String

    var attitude = CMAttitude()
    var motion = CMDeviceMotion()
    motion = motionManager.deviceMotion
    attitude = motion.attitude


    YawLabel.text = NSString (format: "Yaw: %.2f", attitude.yaw) as String 
    PitchLabel.text = NSString (format: "Pitch: %.2f", attitude.pitch) as String
    RollLabel.text = NSString (format: "Roll: %.2f", attitude.roll) as String

    if NSString(string: RollLabel.text!).doubleValue <= -1.6 &&  NSString(string: RollLabel.text!).doubleValue >= -1.2 {
        readOutLabel.text = ""
    }
    else{
        readOutLabel.text = ""
  }

}
}